It’s easy not to think about radon. It’s a colorless, odorless gas that we can’t detect without special equipment, and it has no immediate effects. That doesn’t mean we shouldn’t be worried.
Radon is considered the second leading cause of lung cancer in the U.S., after smoking, causing an estimated 20,000 deaths per year, according to the U.S. Environmental Protection Agency (EPA). This makes radon an even greater risk than secondhand smoking—the number-three cause. For smokers, the cancer risk of radon is increased.
Radon-222 (the number indicating the atomic weight) is a radioactive decay product of uranium-238—which is a common constituent of soils and bedrock, particularly those with granitic geology. Radon has a very short half-life of just 3.8 days, breaking down into polonium-218 and then a string of other short-lived radioactive decay (daughter) products.
Radon itself is not the culprit: it is the solid, charged daughter products of radon that cause problems. They attach to airborne dust particles that we breathe into our lungs. There, they can adhere to our lung linings and emit radioactive alpha particles, which can damage DNA in cells, causing lung cancer.
The primary source of radon in buildings is seepage into basements or through cracks in concrete floor slabs. The underlying bedrock influences the expected radon concentrations, but there is tremendous variability from building to building even in the same area. Radon can also enter homes through well water or municipal water. For all these reasons, EPA recommends testing for radon everywhere.
Radon concentrations are measured in picocuries per liter (pCi/l). While there is no established “safe level,” the need to take action depends on the measured levels in a home. If radon levels are below 2.0 pCi/l, taking action is not recommended, because reducing levels below that is difficult. Between 2.0 and 4.0 pCi/l, EPA recommends that homeowners
consider taking remedial action, and if levels are 4.0 pCi/l or greater, EPA recommends remedial action, particularly as levels get higher and higher. Levels as high as 2,000 pCi/l have been measured; in one such case, the homeowner set off radiation alarms when
entering the nuclear plant where he worked!
Radon mitigation involves a several-part strategy: first to block entry by creating a tight foundation system; second to provide a drainage layer around the foundation and a ventilation stack to passively ventilate the slab and foundation drainage layer; and third to actively depressurize that drainage layer should testing show high radon levels in the house. With this active mitigation strategy, a quiet, durable fan is installed in the passive ventilation stack to keep the slab and foundation drainage layer at negative pressure. Not surprisingly, all this is much easier in new construction than with existing houses.
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